of berlin



Patented Mar. 8, 1932 UNITED STATES PATENT OFFICE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN OOMIPANY, OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE PRODUCTION OF PULP OF HIGH ALPHA CELL'ULOSE CONTENT No Drawing. Application filed. June 17,

This invention relates to the production from various types of raw cellulosic material of cellulose pulps which at the time of their liberation are of high alpha cellulose content. i

In accordance with the process of the present invention, I apply at least two chemical treatments to the raw cellulosic material to effect its conversion into such pulp. The first treatment consists in subjecting the raw cellulosic material to the action of a mercerizing liquor which evidently not only extracts a portion of the non-fibrous constituents of the wood, and more especially the pentosans, but so modifies the constitution of the cellulose fibers that the pulp subsequently obtained is of extremely low solution viscosity. The second treatment consists in cooking the pretreated cellulosic material, preferably after it has been washed, in a sulphurous acid solution containing, if desired, fiber liberating salts, such as the bisulphites, until fiber liberation has been accomplished.

While the process of the present invention is applicable to various raw cellulosic materials used for the production of pulp, including straw and bamboo which are high in pentosan content and resist pulping by the usual acid sulphite process, it will hereinafter be described with specific reference to wood as the raw cellulosic material. The wood is preferably cut into chips such as ordinarily used in pulp manufacture, and the chips are subjected to the action of a mercerizing liquor until they have been completely saturated therewith. Using chips of the size customarily employed in chemical pulpmaking, a steeping of the chips at approximately room temperature in a caustic soda solution of about 18% strength for from ten to twentyfour hours, will result in the penetration of the solution throughout the chips. If desired, a uniform and complete impregnation of the wood may be had with such liquor in a shorter period of time by reducing the wood to chips, fragments, or shavings, of a size much smaller than that of the usual chips. Or the impregnation may be hastened bysteeping the chips in a bath of solution which is maintained under superatmospheric pres- 1930. serm No, 461,855.

sure by compressed gas, such as air, or by hydraulic pumps. It is possible to use caustic soda solutions of less than 18% strength, but in such case it is necessary to cool or refrigerate the solution to below room temperature in order to realize a mercerizing effect. For instance, if a 10% caustic soda solution is employed, it should be kept at a temperature at least as low as 5 to 10 C., in order to realize the desired mercerizing effect. But an 18% or stronger caustic soda solution may be used at above room temperature, say at 70 to 80 C., in which case more rapid penetration of the raw material by the solution is effected, as well as modification of the material generally in the direction of a product of low solutionviscosity. If desired, the treatment with the caustic soda solution may be carried out with such solution maintained at different temperature conditions during the treatment, so that the raw material undergoes two stages or periods of treatment, in one of the stages or periods of which the solution is kept at a sufiiciently low temperature to be mercerizing, and in the other of the stages at a sulficiently higher temperature to modify the raw materials pronouncedly further in the direction of a product of low solution viscosity. The low temperature treatment may precede 0r succeed the high temperature treatment. For example, the raw material may be first steeped in an 18% caustic soda solution at room temperature, and the solution then heated to 70 to 80 C. Or when the initial treatment is with a 10% caustic soda solution at a temperature at least as low as 5 to 10 0., the solution may then be heated or permitted to rise in temperature to that of the room by absorption of heat from the room atmosphere for the second treatment. Such two-stage treatments are advantageous when the caustic soda solution is of insufficient causticity to effect mercerization in the high temperature stage.

The mereerizing liquor may contain chemicals besides caustic soda, such, for example, as sodium sulphide or sodium polysulphide, in which case a portion of the caustic soda may be omitted, as sodium sulphide, too, can

function as a mercerizing agent, although be-' cause it is less active as such than caustic soda, some caustic sodain fact, a preponderant amount of caustic soda-is preferably used. The use of a reducing agent, such as sodium sulphide, sodium sulphite, or the like, in the mercerizing liquor is advantageous, in that such an agent favors the removal of ligneous matter from the wood. For instance, sodium sulphide has been found to be more effective in this respect than caustic soda, both under .the temperature conditions at which mercerization is effected and under higher temperatures. So, too, it has been found desirable to use an oxidizing agent such as hypochlorite in the mercerizing liquor, as such an agent not only exerts a delignifying action on the wood, but tends t6 modify the nature'of the wood "fibers so that the resulting pulp is of extremely low solution viscosity. When an oxidizing agent is present in the mercerizing liquor, 1t is preferable to use a two-stage treatment, for in:

stance, an initial treatment at room temperature or below, and a second treatment at 60 to 100 0., as such a two-stage treatment permits the oxidizing agent to be consumed largely during the low temperature period of the treatment, under which temperature conditions injury to the cellulose fibers by the oxidant is kept at a minimum. In the event that the liquor contains either a reducing or an oxidizing agent, the delignifying action efi'ected on the wood, while sensible, is far too small to cause a liberation of fiber from the wood under the temperature conditions employed.

Irrespective of Whether the mercerizing liquor contains only caustic soda or contains reducing or oxidizing agents in addition to caustic soda, the initial treatment profoundly affects both the wood and the nature of the cellulose fibers which it is desired to free therefrom. Thus, the mercerizing liquor extracts from the wood considerable of its pentosan content and additionally soalters the nature of the cellulose fibers that when they are subsequently liberated as a pulp, the pulp is characterized by its low solution viscosity. In fact, the mercerizing treatmentv leaves its telltale marks on the finished pulp. which has comparatively poor physical paper-making characteristics. Because of its high purity, low solution viscosity, and other desirable characteristics, it is useful to advantage, not only in the preparation of cellulose derivatives, but also in papermaking furnishes when high strength in the finished paper is not a primary consideration. It is further valuable in papermaking furnishes, for the reason that it enhances the bulk and improves the flatness of the resulting paper.

The mercerized chips are preferably washed, but the Washing operation need not be carried to a point where all the caustic soda is removed from the chips. The fact that the chips may be cooked in a bisulphite liquor to complete fiber liberation does away with the necessity of complete washing, particularly when a mercerizing liquor containing only caustic soda is used, as a bisulphite liquor of the composition desired may be had from washing the chips to a predetermined residual caustic soda content, and then adding a sulphurous acid solution thereto. Inasmuch as almost all of the caustic soda present in the mercerizing liquor resulting from thetreatment of the chips is in active condition, the resulting bisulphiteliquor is practically as good as one prepared from entirely fresh chemicals. Liquors of various com ositions may be used under a variety of con itions in cooking the mercerized chips to complete fiber liberation. For instance, a bisulphite liquor containing 1% combined S6 and 5% free SO may be used, in which case cooking may be carried out for six to eight hours at a maximum temperature of 285 The over-all yield of pulp based on the-weight of dry wood is about 48%. The pulp has an alpha cellulose content of about 96% and a solution viscosity of about 0.3, whereas the solution viscosities of the usual commercial wood pulps, such as draft or sulphite, or wood pulps refined to high alpha cellulose content, are vastly higher. may also be obtained by cookingin solutions of only sulphurous acid, or in sulphurous acid solutions containingsodium sulphite'or sodium acid sulphate. For instance, fiber liberationsmay be accomplished by cooking for six to eight hours in a 5% sulphurous acid solution at a-maximum temperature of 260 F. The resulting pulp may be directly bleached, but for the preservation of maximum alpha cellulose content therein, it is preferred to precede the'bleaching operation by light chemical refining treatments. To this end, the pulp may be initially treated at about room temperature with chlorine water containing'about 2% .to 3% chlorine, based on the'weight of dry fiber,whereupon, after all the chlorine has been consumed, the pulp may be digested in a weak alkaline solution, e. g., a solution containing 2% to 3% caustic soda or sodium carbonate, basedon the weight of dry fiber, at temperatures of, say, from 100 to 150 C., to remove chlorine reaction productsf The pulp may then be washed and finally bleached to pure whiteness in a hypochlorite bleach liquor containing only 2% to' F. to produce pulp.

chlorine gas or chlorine waterin order to chlorinate ligneous matter present therein and thus render such matter more readily soluble in the mercerizing liquor. Or the raw material may be digested at elevated temperatures, preferably not above 150 C., in water or in dilute solutions of alkali or of salts such as sodium sulphite, as such digestion results in a partial removal of ligneous matter and pentosans from the raw material, without, however, producing fiber liberation.

By carrying out any one of the foregoing treatments on the raw material before steeping it in a mercerizing liquor, not only is the porosity of the raw material increased so that it is penetrated more rapidly by the liquor, but the time of contact with such liquor may be cut down materially in producing a pulp of the desired characteristics. Another treatment whi'ch fits in between the two main treatments is a digestion of the cellulosic material in a weak solution of alkali, as such a solution may conveniently and economically be one prepared by adding water to the cellulosic material containing residual alkali from the mercerizing treatment. In such case, after the mercerizing treatment, the cellulosic material may be drained or washed to the desired residual alkali content and water then added thereto to produce a solution of low alkalinity. The cellulosic material may then be cooked in the weakly alkaline solution, which, while it does remove some ligneous matter and assist in the production of pulp of low solution viscosity, cannot effect a perceptible pulping of the cellulosic material. As a matter of fact, it is undesirable to cook at high temperatures, say above 80 0., in a strong solution of alkali, which, entirely apart from its own tendency to liberate pulp, tends to impede subsequent fiber liberation by cooking in sulphurous acid solutions. After cooking in the dilute alkaline solution, the material is washed, preferably completely free of spent solutions, before it is cooked to complete fiber liberation in a sulphurous acid solution.

Other chemical treatments may be applied to the cellulosic material either before or after the mercerizing treatment and/or the cook in sulphurous acid solution without departing from the present inventign.

An important advantage of the process of the present invention, in addition to those enumerated, is that it may be practised in connection with various types of woods, such as spruce, poplar, hardwood, and pine etc. When the raw wood is high in resins, the initial treatment of the raw wood with a strongly caustic liquor at either low or high temperature makes possible such a marked reduction of resins in the wood that subsequent cooking of the wood in a sulphurous acid solution to complete fiber liberation results in a pulp capable of being readily refined arid/or cellulosic material with a mercerizing liquor, Y

and then cooking such material to complete fiber liberation in a sulphurous acid solution.

2. A process which comprises steeping raw cellulosic material in a bath of mercerizing liquor until such material has been completely penetrated by such liquor, removing the material from the bath, and cooking it to complete fiber liberation in a sulphurous acid solution.

3. A process which comprises treating raw cellulosicmaterial with a mercerizing llquor, washing the treated material, and cooking it to complete fiber liberation in a sulphurous acid solution.

4. A process which comprises treating. raw cellulosic material with a mercerizing liquor, washing the treated material incompletely free from alkali, adding a sulphurous acid solution to such material to form bisulphite in situ therein, and cooking to complete fiber liberation in such solution.

5. A process which comprises treating raw cellulosic material with a'mercerizing liquor, washing the treated material incompletely free from alkali, adding water to the material to form a dilute alkaline solution, cooking the material short of fiber liberation in the solution, and then cooking to complete fiber liberation in a sulphurous acid solution.

6. A process which comprises steeping raw cellulosic material in a caustic soda solution under mercerizing and non-mercerizing temperature conditions, and then cooking such material to complete fiber liberation in a sulphurous acid solution.

7 A process which comprises steeping raw cellulosic material in a caustic soda solution at a sufiiciently low temperature to be mercerizing and at much higher temperature, and then cooking such material to complete fiber liberation in a sulphurous acid solution.

8. A process which comprises steeping raw cellulosic material in a caustic soda solution containing an oxidant at a sufficiently low temperature to be mercerizing until the oxidant is largely consumed, heating the solution to above the mercerizing temperature, and then cooking the material to complete fiber liberation in a sulphurous acid solution.

9. A process which comprises treating raw celluloslc material with a mercerizing liquor, and then cooking such material in a bisulphite solution to efit'ect fiber liberation.

In testimony whereof I have afiixed my signature.

GEORGE A. RICHTER. 

